What is "brown spar"

Brown \Brown\ (broun), a. [Compar. Browner; superl. Brownest.] [OE. brun, broun, AS. br?n; akin to D. bruin, OHG. br?n, Icel. br?nn, Sw. brun, Dan. bruun, G. braun, Lith. brunas, Skr. babhru. [root]93, 253. Cf. Bruin, Beaver, Burnish, Brunette.] Of a dark color, of various shades between black and red or yellow. Cheeks brown as the oak leaves. --Longfellow. Brown Bess, the old regulation flintlock smoothbore musket, with bronzed barrel, formerly used in the British army. Brown bread

1. Dark colored bread; esp. a kind made of unbolted wheat flour, sometimes called in the United States Graham bread. ``He would mouth with a beggar though she smelt brown bread and garlic.''
   --Shak.

2. Dark colored bread made of rye meal and Indian meal, or of wheat and rye or Indian; rye and Indian bread. [U.S.]

   Brown coal, wood coal. See Lignite.

   Brown hematite or Brown iron ore (Min.), the hydrous iron oxide, limonite, which has a brown streak. See Limonite.

   Brown holland. See under Holland.

   Brown paper, dark colored paper, esp. coarse wrapping paper, made of unbleached materials.

   Brown spar (Min.), a ferruginous variety of dolomite, in part identical with ankerite.

   Brown stone. See Brownstone.

   Brown stout, a strong kind of porter or malt liquor.

   Brown study, a state of mental abstraction or serious reverie.
   --W. Irving.

n. (context mineralogy English) A ferruginous variety of dolomite, in part identical with ankerite.